Fig. 4.

Allometry of the spearhead-like particles. Variance in stalk width and spearhead width are both ≈3.6% of those respective means. Variance in spearhead length, by contrast, is >15% of mean spearhead length, suggesting that spearhead-like particles continue to grow lengthwise after they reach a (perhaps itinerantly) maximum width and maintain a constant proportion between stalk and spearhead. This allometry is consistent with the sense of elongation required by assumed epitactic growth forming the tipward-convex, surface “step” features on both stalk and spearheads.